The invention relates to an oscillator comprising a (first) amplifier element which has a control terminal and a main current path ending in a first and a second output terminal, the oscillator including a network through which the first output terminal of the (first) amplifier element is fed back to the control terminal of the (first) amplifier element by a series-arranged piezoelectric oscillation element, and including a (first) output dipole (i.e., a reactive circuit element, such as a resonant LC circuit or inductor); coupled to the first output terminal of the (first) amplifier element and including a DC current defining element coupled to the second output terminal of the (first) amplifier element. For simplicity, a reactive circuit element will be referred to hereinafter and in the claims as a dipole. A dipole shall be understood to mean a dipolar electrical energy storage element, such as a capacitive, inductive or resonant LC circuit element.
From the monograph "Oscillator Design Handbook" by Gary A. Breed, published 1990 by Cardiff Publishing Company, more particularly pp. 55 to 60, crystal oscillators of various types are known. A so called "Pierce oscillator" has in its simplest embodiment an npn transistor as an amplifier element, whose collector and base are coupled to each other via a crystal (quartz crystal). The collector is furthermore connected via an inductor to a positive supply voltage terminal and represents the output of the "Pierce oscillator". Furthermore are connected to ground the collector of the transistor, via a first capacitor which may be tunable, the base, via a second capacitor and the emitter of the transistor via the parallel circuit of an emitter resistor having a very large capacitance. The base is further connected to the positive supply voltage terminal via a dropping resistor. In a modification, a parallel resonant circuit having an inductor and a--tunably arranged--capacitor capacitor may take the place of the inductor at the collector. This antiresonant circuit can be tuned to the oscillation frequency of the crystal.
This "Pierce oscillator" is designated as having the best frequency stability of all the crystal oscillators discussed in the "Oscillator Design Handbook" it is true, but for a miniaturized integration on a semiconductor body, the very large capacitor in the emitter circuit i.e. between emitter and ground, is highly annoying, because it takes up an unproportionally large space on the semiconductor body. This forms a large hindrance as to the construction, especially for small, light electronic devices such as, for example, radio pagers (pagers).